The microwave outdoor radio device (hereinafter, may be simply referred to as “outdoor device”) is installed at a high location by a support pillar, and connected to an indoor device installed at a low location by a coaxial cable. JP2011-249988A (hereinafter, referred to as Patent Literature 1) discloses an antenna device configured in a manner in which an input/output coaxial cable terminal is positioned to tilt by θ° from a vertically downward direction when an outdoor device is connected to a horizontally polarized wave antenna, and the input/output coaxial cable terminal is positioned to tilt by (90−θ)° from the vertically downward direction when the outdoor device is connected to a vertically polarized wave antenna. For example, in the case of θ=45°, both when the outdoor device is connected to the horizontally polarized wave antenna and when the outdoor device is connected to the vertically polarized wave antenna, the input/output coaxial cable terminal tilts by 45° from the vertically downward direction.